Beta-gamma directional correlation in Eu¹⁵⁴

Abstract

The directional correlation between the nonunique first-forbidden outer beta group of end-point energy 1855 kev in Eu¹⁵⁴ and the 123-kev cascade gamma ray in Gd¹⁵⁴ has been measured at twelve beta-ray energies. The measured beta-gamma correlation coefficient e ranges from -(0.222±0.013) to -(0.314±0.017) in the beta-energy interval 1150 to 1700 kev, after correcting for the attenuation due to the extranuclear field effect by measuring the attenuation factor G₂=0.71±0.03 in the 1277-123-kev gamma-gamma cascade in Gd¹⁵⁴. The correlation coefficient e varies almost as (p²/W) in this energy interval. The attenuation effect on the beta-gamma correlation coefficient under different physical conditions of the source has been demonstrated experimentally. An analysis of the data by an electronic computer leads to values of the matrix element ratios (Kotani's notation): z=1, x=0.5±0.05, u=0±0.05, and Y=1.55±0.10. It is concluded that the "modified B_ij approximation" is reasonably valid in this beta decay.